Products susceptible to spoilage, such as processed foods, nuts and sliced fruits and vegetables, are often placed in hermetically sealed packaging which has been flushed with an inert gas, such as nitrogen or argon, to achieve an oxygen concentration within the packaging of less than about 3% and thereby prolong the shelf-life of the product. Such packaging is commonly known as controlled atmosphere packaging (CAP) or modified atmosphere packaging (MAP).
Leaks in the packaging can significantly reduce the anticipated shelf life, resulting in undesired spoilage. Hence, proper quality control efforts for CAP/MAP typically involve at least periodic testing of packaging to determine if the packaging has any leaks.
A variety of instruments and methods are known for detecting leaks in hermetically sealed packaging. Leak detection typically involves the creation of a pressure differential between the pressure inside the packaging (internal pressure) and the pressure outside the packaging (external pressure)—such as by compressing the packaging or pulling a vacuum in the atmosphere surrounding the packaging, followed by the detection of any change in a given variable which could be correlated to the presence of a leak in the packaging. Specific examples include submersion of packaging into a liquid and detecting any liquid within the packaging (U.S. Pat. No. 6,763,702 issued to Allen Chien et al.), squeezing packaging and detecting any pressure decay (U.S. Pat. No. 6,427,524 issued to Frank Raspante et al.), squeezing packaging and detecting any volume decay (U.S. Pat. No. 5,533,385 issued to William Frievalt) and placing packaging within a vacuum chamber and detecting any loss of vacuum (U.S. Pat. No. 5,150,605 issued to Edwin Simpson).
Leaks in hermetically sealed packaging typically result from (i) the presence of a pinhole in the packaging material created during manufacture of the packaging material or puncturing of the packaging during the form, fill and/or seal process (commonly known as a sidewall leak), or (ii) the presence of a channel through a seal in the packaging created by inadequate sealing of the filled packaging (commonly known as seal leaks). In the event leaks are detected in an unacceptable number of packages, the first step in correcting the problem is to identify whether the leaks are predominantly seal leaks or sidewall leaks.
While the instruments and techniques described above are generally effective for detecting leaks in hermetically sealed packaging, none are capable of detecting the presence of a leak and reliably reporting the location of the leak as between a seal leak and a sidewall leak.